1. Field of the Invention
The present invention relates to a cryptographic module and an IC card, and particularly, to a cryptographic module and an IC card that are resistant to power analysis.
2. Description of the Related Art
Conventionally, cryptographic technology for the purpose of protecting confidential data is used in various systems.
Cryptographic technology is used even in systems currently in practical and widespread use such as electronic money systems and transportation systems due to the handling therein of private information, balance information and other confidential data. In addition, various techniques have been proposed in regards to such cryptographic technology.
Among such various proposed techniques, for example, in addition to those regarding cryptographic operations technology such as the technique disclosed in Japanese Patent Laid-Open No. 2000-56679 in regards to the acceleration of key schedules in DES (Data Encryption Standard) that is an encryption method, recently, there are techniques regarding countermeasures to so-called power analysis attacks such as the technique disclosed in Japanese Patent Laid-Open No. 2005-31471.
The cryptographic device designed to counter power analysis attacks disclosed in aforementioned Japanese Patent Laid-Open No. 2005-31471 is configured so as to include a register that retains data to be subjected to cryptographic operations and a register that retains reverse data thereof. For instance, with a CMOS, power is consumed dependent on changes in data.
However, in such a cryptographic device, contents saved in the register are data to be used in normal cryptographic operations. Therefore, the data is completely unhidden. In addition, even if reverse data is retained as described above, the power consumed by the register retaining normal data and the power consumed by the register retaining reverse data do not necessarily cancel out each other. As a result, when coming under a power analysis attack, there is a risk that confidential data to be used in cryptographic operations will be retrieved.